Leak detector for the protective well of a thermal instrument sensitive element



F. W. HAMPSON LEAK DETECTOR FOR THE PROTECTIVE WELL OF A THERMAL INSTRUMENT SENSITIVE ELEMENT Filed May 24, 1945 Aug. 10, 1948.

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BY 64 M ATTORNEYS Patented Aug. 10, 1948 orr es LEAK DETECTOR FOR THE PROTECTIVE WELL F A'THERMAL IN STRUMENTSEN SITIVE ELElVIENT Frederick'W. Hampson, Holyoke, 'Mass.,-assigmor Plating Processes Corporation; Mass, a corporation of'Massaohusetts Hal-yoke,

Application May 24, 1'945,-S erialNo. 59552.7

This invention relates to a protective well for use with the sensitive bulb of a thermal instrument and more particularly when said instrument is employed in an electrolyte bath for recording or indicating temperatures thereof. It is desirable not only to protect the sensitiveelement of the instrument from attack by the electrolyte of the bath, but also to give a warning of any break down in said protective means so that the sensitive element may be rescued in time to prevent serious injury thereto and to replace the same with effective protective means. The object of the invention is to provide a novel and improved construction of such a protective means which will be reliable in operation-simple and economical in manufacture, and convenient to use.

The single figure of the drawing shows in section a part of an electrolyte bath with my improved. protective well mounted therein.

Referring to said drawing i indicates the metal wall for the bath tank partially filled with electrolyte 2. Mounted at the top of said wall l is a supporting bracket 3 preferably of plastic material so as to be an electrical insulator which is fastened to the wall l by angle iron 5 and screws 5. A bolt 6 secures the'bracket 3 to the angle iron 4 so as to eXtend ho-rizontally over the bath as shown.

The protective well indicated generally at 1 is suspended from the bracket 3 so as to extend downwardly into the electrolyte of the bath as shown. This well is mounted on and hung from bracketfi by means of a hollow fitting d which is clamped to bracket 3 between its shoulder 9 and a receptacle is screwed on its upper end. The lower end of said fitting 8 is tapered toenter the upper flared open end of the'well l and a ing 53 is remova'bly fitted into the upper end of the fitting 8 for spacing a capillary tube M of the usualtype of metal bulb is which is received in the well l and the said capillary tube It is eX- tended laterally through the side of the receptacle it to the recording or indicating part of the thermal instrument (not shown). The bulb I5 and its tube Hi are of metal while the other parts associated therewith viz. the fitting 8, nut ll, receptacle it, and its cover [2 are all of insulating material such as hardened plastic.

The protective well i is of special fabrication made up of an inner tubular core it closed at its bottom end and with a liquid tight Wall 3 Claims. (Cl. 177- 311) throughout. The material for the tubular core it may be any suitable electrically insulating material capable of being machined or formed with a very thin wall which will hold up for the subsequent operations to beperformed on it. In selecting a plastic for this core 16 consideration should be given to it's tensile strength, softening temperature, toughness and resiliency. it should of 'coursebe capable of Withstan'ding' the heat of the bath in which it is used Without breaking down. I have found that a very suit able material for this purpose is Vinylidene chloride and my inner core it is preferably of this material.

In order to favor the conduction of heat through the plastic inner core-126 its Wall is formed as thin-as practical and its-f formation maybe accomplished by molding the same on a supporting mandril. The lower part lfi'a of the tubular core it is preferably reduced to a slightly smaller internal diameter-than the upper part thereof and said'lower part lifiUWillGlIlbI'ZLC-llh'fi bulb i5 snugly with a .slidable and removable 'fit. Th upper and larger "diameter part ofthe core' wall l6 may be about .05 to I06"'tin thickness while the lower bulb embracing part Ilia may-be .03" to .04" in thickness] the'purpose of this snug embracement as well a's reduced thinness being to :facilitate the conductiono'f heat from the electrolyte bath Zto the bulb I 5.

The tubular core it when initially formed is of such thinness as to be very easily collapsedand hardly has 'sufiicien't body to sustain its own shape unsupported. For "the purpose of reinforcing it and making it self sustaining in use as a protective well I' deposit on the outside of said core wall lfi'one or more coatings of metal which will give the necessary strength to the core '55 'and'yet will not appreciably reduce its heat conductive property since i the particular metal ch'osen for the coating maybean especially Preferably '-I {apply three successive thin coatings of metal on the outside' 'of the plastic core tube l6. lhe first coat indicated at H on the drawing is primarily for the purpose of rendermg the plastic wall electrically conductive for the electro-deposition thereon of subsequent metal coatings. This primary coat may be applied by spraying or immersion, the latter method being preferable and a suitable metal for this primary coat is silver because of its ability to take a uniform deposit by immersion, its good adhesion qualities and its heat and electrical conductivity.

Upon the primary coat I! is then electro-deposited a thin coat of copper marked 18 on the drawing, copper being the metal preferred because it is soft, easy to plate, and a metal that bridges any slight open spaces easily. It is also a good electrical and heat conductor.

The third of final coat marked 19 on the drawing should be a metal that resists attack from the bath or electrolyte in which the protective well is to be used. For example an outside coat of nickel would be suitable for alkaline solutions, lead could be used for certain types of acid solutions including chromic acid, cupric acid, etc., and iron would be suitable for cyanide solutions, alkaline cleaners, etc. When ing of heat conductive metal deposited thereon to reinforce said plastic material to self-sustainin; shape and to provide a highly heat conductive surface for said well, and an electrical signalling circuit, one side of which is connected to said bulb and the other side of which is connected to the outer metallic coating of said well immersed 4 in said bath.

iron is used, an extra outside thin coating of nickel could be added thereto to retard oxidization.

The third and final protective coating l 9 is also electrodeposi-ted and like each of the previous coatings is in a very thin layer of approximately .005" thickness.

The advantages of such protective means for the bulb I5 are that it furnishes an easily removable and replaceable guard for thesensitive bulb in keeping it out of direct contact with the electrolyte of the bath and in good heat conductive relation thereto. The relatively soft characteristic of such a plastic as described'permits the bulb to fit very tightly in its lower pocket without scratching or other possible injury thereto.

In the manner described the sensitive bulb I5 is protected from direct contact with the electrolyte 2 of the bath, but in the event said protective well should break down or develop a leak therethrough it is desirable that a warning of such condition be given. It is a common practice in such cases to provide an electric signalling circuit which will be closed by any leakage through the well wall. Such a circuit is herein provided and is shown in the drawing as comprising. the battery 20, relay 2!, and signal device 22 of the usual character for giving a signal when any electrolyte penetrates the wall of the protective well 1 and comes into contact with the metal of the bulb l5. Such a contact of leaking electrolyte will close the circuit, one side of which is wire 23 connected to metal tube 14 and the other side of which is wire 24 in conducting relation to the bath of electrolyte 2.

I claim:

'1. In a leak detector system in combination, a bath of electrolyte, a thermally responsive instrument comprising, a metal bulb in heat exchange relationship with said bath, a protective well to prevent direct contact between said bath and bulb comprising a liquid-tight preformed tube with closed bottom extending into said bath and having an inside diameter substantially the same as said bulb adapted to receive therein said bulb in snug substantially form fitting removable relation, said well being formed of a plastic insulating material with an extremely thin wall, a coat- 2. In a leak detector system in combination, a

a as saidbulb adapted to receive therein said bulb in snug substantially form fitting removable relation, said well being formed of a plastic insulating material with an extremely thin wall, successive coatings of different heat conductive metals deposited thereon to reinforce said plastic material to self-sustaining shape and to provide a highly heat conductive surface for said well the outermost coating of which is resistant to attack by said bath, and an electrical signalling circuit, one side of which is connected to said bulb and the other side of which is connected to the outer metallic coating of said well immersed in said bath.

3. For use in a bath of electrolyte a thermosensitive bulb having a wall of thin electrically conductive material and a capillary tube of similar material attached to the bulb, in combination with a liquid-tight preformed protective well with closed bottom for the encasement of said bulb in a bath of electrolyte, said well including a reduced lower portion of substantially the same conformation as said bulb and adapted to receive said bulb in snug substantially form fitting removabie relation, the inner wall of said well being formed of an extremely thin plastic wall of insulating material, and a coating of heat conductive and electrically conductive metal deposited on said plastic wall to reinforce the same.

FREDERICK W. HAMPS ON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 199,442 Huddleston Jan. 22, 1878 738,960 Vaughan Sept. 15, 1903 1,538,042 Hurlburt May 19, 1925 1,801,791 Breisky et al. Apr. 21, 1931 1,983,166 Chaney Dec. 4, 1934 2,067,440 Finney Jan. 12, 1937 FOREIGN PATENTS Number Country Date 547,840 Great Britain Sept. 14, 1942 

